Fruit and vegetable pricing in supermarkets
The Problem
Fruit and vegetable consumption in the UK is below recommended levels, with only one third of adults consuming at least five portions per day. Fruit and vegetable consumption patterns are not equal around the country, and less wealthy households tend to consume fewer portions per day. Low consumption of fruit and vegetables is associated with increased risk of non-communicable diseases, including cancer and cardiovascular disease.
The high cost of fruits and vegetables has been identified by consumers as a barrier to increasing their consumption. To address this issue, studies have investigated whether applying price promotions to fruits and vegetables leads to an increase in their purchasing or consumption, and the majority have found them to be effective in doing so.
However, the current evidence base consists mostly of hypothetical modelling studies, real-world implementation studies with only a small sample of stores, or studies specifically focused on lower socio-economic groups. The current study will investigate the effectiveness of fruit and vegetable discounts across a large sample of stores belonging to a UK-based retailer, varying in their size, location and socio-economic status.
Research question
- What is the impact on sales of price discounts on fruit and vegetables?
- Does the impact of price discounts vary by the size, location or socio-economic status of the store?
The Intervention
The implementation of a membership programme which provides enlisted customers with discounts on select products, including fruit and vegetables.
Setting
Supermarket stores belonging to a large UK-based supermarket.
Key Outcomes
The key outcome variable is the weekly aggregate sales of fruit and vegetables by store, defined by total weight (kg), total value (£) and total number of transactions.
Preliminary or pilot studies
A pilot study will analyse data on aggregate sales of fruit and vegetables for members and non-members from two stores over a two year period. We will observe patterns in the dataset, isolate key variables associated with changes in trend, and design Interrupted Time Series models that we will use in our evaluation. The purpose of this pilot is to answer any questions that may also be true of the full dataset, to inform the drafting of a research protocol for this study.
Evaluation design
An Interrupted Time Series analysis will assess the effect of introducing member-price discounts on fruits and vegetables, on their weekly sales. This quasi-experimental design will track the trend in weekly fruit and vegetable sales over a two-year period (February 2022 to February 2024), and compare the trends before and after the introduction of the membership programme. The weekly sales data will be divided into purchases made with a membership card and purchases made without, with the latter acting as a comparator series. This approach will allow for the evaluation of how effective the member-pricing of fruits and vegetables was in encouraging customers to purchase more of these products, and whether these effects were specific to those enrolled in the membership programme. We will assess differences in effect size by store size, socio-economic status and location.
Sample size
Data will be provided by the retailer for a total of 90 stores spread across England. The 90 stores will be selected so that there is one store from each of the 2 x 5 x 9 strata consisting of:
- Size of store (small or large)
- Quintile of Index of Multiple Deprivation
- Government Office Region of England
Process evaluation
Plans are in development for a process evaluation involving interviews with members of staff from the supermarket chain.
Proposed outputs
We will publish the full protocol in an open access registry. We will publish the findings of the evaluation in a peer-reviewed journal. The results will contribute to the final SALIENT report and policy briefs, which will be disseminated to policymakers in the UK.
Timescale
Pilot data analysis will take place in summer 2024, with the protocol and full evaluation following in late 2024.
Our Team
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Mike Rayner
Researcher
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Alice O'Hagan
Research Assistant